Hydrocarbon wells, horizontal wells in particular, typically have sections of wellscreens with a perforated inner tube and an overlying screen portion. The purpose of the screen is to block the flow of particulate matter into the interior of the perforated inner tube, which connects to production tubing. Even with the wellscreen, some contaminants and other particulate matter can still enter the production tubing. The particulate matter usually occurs naturally or is part of the drilling and production process. As the production fluids are recovered, the particulate matter is also recovered at the surface. The particulate matter causes a number of problems in that the material is usually abrasive reducing the life of any associated production equipment. By controlling and reducing the amount of particulate matter that is pumped to the surface, overall production costs are reduced.
Even though the particulate matter may be too large to be produced, the particulate matter may cause problems downhole at the wellscreens. As the well fluids are produced, the larger particulate matter is trapped in the filter element of the wellscreens. Over the life of the well as more and more particulate matter is trapped, the filter elements will become clogged and restrict flow of the well fluids to the surface.
A method of reducing the inflow of particulate matter before it reaches the wellscreens is to pack gravel or sand in the annular area between the wellscreen and the wellbore. Packing gravel or sand in the annulus provides the producing formation with a stabilizing force to prevent any material around the annulus from collapsing and producing undesired particulate matter. The packed gravel also provides a pre-filter to stop the flow of particulate matter before it reaches the wellscreen.
In typical gravel packing operations, a screen and a packer are run into the wellbore together. Once the screen and packer are properly located, the packer is set so that it forms a seal between wellbore and the screen and isolates the region above the packer from the region below the packer. The screen is also attached to the packer so that it hangs down in the wellbore, which forms an annular region around the exterior portion of the screen. The bottom of the screen is sealed so that any fluid that enters the screen must pass through the screening or filtering material. The upper end of the screen is usually referred to as the heel and the lower end of the screen is usually referred to as the toe of the well.
Once the screen and packer are run into the wellbore but before they are run to their intended final location, a washpipe subassembly is put together at the surface and is then run downhole through the packer and into the screen. The run-in continues until a crossover tool on the washpipe subassembly lands in the packer. The entire assembly is then ready to be run into the wellbore to its intended depth.
Once the assembly of the screen, packer, washpipe, and crossover tool reaches its intended depth in the wellbore, a ball is pumped downhole to the crossover tool. The ball lands on one of two seats in the crossover tool. Once the ball lands on the first seat, pressure is applied from the surface across the ball and seat to set the packer and to shift a sleeve in the crossover tool. With the sleeve open, fluid, typically gravel slurry, may be pumped down the well through the washpipe. Physical manipulation of the crossover tool by raising the washpipe is required to position it properly relative to the screen and packer assembly so that fluid circulation can take place. When the slurry reaches the crossover tool, the gravel slurry is blocked by the ball and seat that was previously landed in the crossover tool. Instead, the ball and seat causes the gravel slurry to exit the crossover tool through a port that directs all fluid flow from inside of the washpipe above the packer to the outside of the washpipe and screen below the packer and into the annular space outside of the screen.
As the slurry travels from the heel of the well toward the toe along the outside of the screen, an alpha wave begins that deposits gravel from the heel towards the toe. All the while, the transport fluid that carries the gravel in the slurry drains inside through the screen. As the fluid drains into the interior of the screen, it becomes increasingly difficult to pump the slurry down the wellbore. Once a certain portion of the screen is covered, the gravel starts building back from the toe towards the heel in a beta wave to completely pack off the screen from approximately its furthest point of deposit towards the heel. As the gravel fills back towards the heel, the pressure in the formation increases.
The crossover tool has a second port that allows fluid to flow from the interior area of the screen below the packer to an annular area around the exterior of the washpipe but above the packer.
After the annular area around the screen has been packed with gravel, the crossover tool is again moved relative the screen and packer assembly to allow for fluid circulation to remove any slurry remaining in the washpipe above the packer. The flushed slurry is then disposed of at the surface. Then, a second ball may be pumped down the well to land in a second ball seat in the crossover tool. After the second ball has seated, pressure is applied from the surface to shift the sleeve in the crossover tool a second time as well as to seal off the internal bore of the crossover tool and to open a sleeve in a second location. Once the sleeve is shifted and is sealed in a second location, wellbore fluid from the surface flowing through the washpipe may be directed into an internal flowpath within the crossover tool and then back into the interior of the washpipe, thereby bypassing both the first and the second balls and seats. Once the fluid has been redirected to stay in the washpipe, the operator may reposition the washpipe and begin to acidize or otherwise treat the wellbore.
In the current system, fluid flow through the interior is limited by forcing the fluid to travel through a micro-annulus, which is the only path available in crossover tool. The only alternative is to reverse the washpipe and crossover tool completely out of the hole and run-in with an unobstructed washpipe. The additional trip out of the hole and then back in leads to additional time and expense in completing the well.
When typical seals as described above are used, care must be taken so that each lower seal and seat has a diameter that is smaller than the seal and seat above it. Such an inverted wedding cake arrangement helps to insure that the operator does not attempt to force a device through a seal that is too small thereby damaging the seal.
Such an arrangement may limit the diameter of the bore through a tubular. Also, typically once a device seals on a particular seat, the seat cannot be reused. When several seal and seats are needed in close proximity, the utility of the tool or tools may be limited.